Generally, electric hot water heaters use electrical power as a heat source and can be classified into an input type, an instantaneous type, and a low temperature type. The input type is a water heating type having a heating element such as a Ni-chrome wire wrapped in a copper pipe with an insulator such as mica, which is putted into a bathtub or a simple hot water heater. The instantaneous type is a water heating type in which the coils such as the Ni-chrome wire are isolated and are formed into multiple layers. Water is heated while the water passes through the coil. Meanwhile, the low-temperature type is a water heating type in which the Ni-chrome wire is enclosed in a copper tube and the enclosed copper tube is installed within a low-temperature bath. The low-temperature bath is maintained at a constant temperature by using a thermostat.
Since such electric hot water heaters may use electrical power, the efficiency of converting the electric energy into the heat energy is very important in order to save the electrical power.
As an example of the prior art, Korean Registered Patent Publication No. 10-1269729 registered on May 30, 2013 discloses a water boiler.